Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
Food waste and other putrescible organic waste is a major contributor to the cost of waste disposal. This is due largely to the present need to transport such wastes to specific landfill sites which are often at significant distances from the sites of the waste production. In addition, the disposal of wastes such as food waste and other putrescible organic waste is particularly undesirable due to their high water and nutrient content, leading to the release of organic acids and other compounds during anaerobic decomposition which are major contributors to the negative environmental impacts associated with landfills (Recycled Organics Unit, 2001a, Greenhouse gas emissions from composting facilities, Report for Central Coast Waste Board, NSW, September 2001). Indeed, food waste is the second largest source of methane in landfills (behind paper and cardboard) (US EPA, 1998, Greenhouse gas emissions from management of selected materials in municipal solid waste, United States Environmental Protection Agency.). The nutrients present in food waste also contribute to the high nutrient and heavy metal loadings in landfill leachate, and is a major contributor to groundwater and surface water contamination in regions with unlined landfills (Russel and Higer, 1988, Assessment of groundwater contamination near Lantana landfill, southeast Florida, Ground Water, 26(2): 156-164; Borden and Yunoschak, 1990, Ground and surface water quality impacts of North Carolina sanitary landfills. Water Resources Bulletin, 26(2): 269-277; Assmuth and Strandberg, 1993, Groundwater contamination at Finnish landfills, Water, Air and Soil Pollution, 69 (1/2):179-199).
In addition to the environmental concerns regarding the landfill disposal of putrescible food and organic wastes, in many countries including Australia, the available landfills are reaching capacity. For example, in Sydney, present landfill capacity for putrescible food and organic wastes in the Greater Sydney Region is expected to be exhausted by 2011, based upon current levels of waste generation and recycling rates (Wright, 2000, Independent Public Assessment—Landfill Capacity and Demand, Report prepared for the Minister of Urban Affairs and Planning, State Government of NSW, September 2000). Such shortages of landfill sites, and the resistance of communities to the establishment of new landfill sites on health, environmental and monetary concerns, is urgently impelling the need to divert recyclable wastes from landfill. Indeed, many Governments have now developed policies to reduce landfill disposal of putrescible food and organic wastes (e.g., the NSW Government policies, ‘Waste Not’ Development Control Plan (DCP) and Waste Reduction and Procurement Policy). However, the meaningful implementation of these policies mandates the identification and development of practical alternatives to landfill disposal.
The present invention is directed at the provision of a simple and cost effective waste treatment apparatus, which may be readily used by waste producers, to decompose food and other putrescible organic wastes to a useful composted waste material product and thereby divert such wastes from landfill disposal. The composted waste material product can be used to improve soils, plants and the environment in which we live.
There are four main types of composting systems that have been devised for commercial purposes, however, hybrid systems are also available. The four main systems can be categorized as follows:
A windrow system: this is an open system and the material to be composted is piled in long rows. These are aerated by forced convection or by frequent turning using a mechanical agitator system.
An enclosed static stack system: air is forced up through the pile of the material to be composted, which is enclosed is some type of vessel. This is a batch process in which the vessel is loaded and unloaded once for each composting cycle.
An agitated bay system: these systems primarily utilize U-shaped channels or bays. Material to be composted is often added semi-continuously and periodically agitated and moved by mechanical means. However, primary aeration is often achieved via forced air movement.
Continuous or semi-continuous in-vessel composting systems: in these systems the material to be composted is fed in one end (side, top or bottom) of the composting systems and exits continuously from the other.
Numerous examples of the above systems are currently being produced and are illustrated in “The Practical Handbook of Compost Engineering”, Roger T Haug, Lewis Publishers, 1993 (ISBN 0-87371-373-7).
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
An object of the present invention, at least in a preferred embodiment, is to provide an in-vessel, semi-continuous and generally vertical composting system, which provides an efficient alternative to existing composting systems.